Heat treatment of surface active reagents in flotation

ABSTRACT

1, 041, 547. Separating minerals by flotation. ESSO RESEARCH &amp; ENGINEERING CO. May 28. 1965 [June 11, 1964; Dec.23, 1964; April 29, 1965], Nos. 24276/64; 52178/64; and 18139/65. Heading B2H. Coal or other mineral material is separated from an aqueous slurry (or suspension) by adding to the slurry a water immiscible organic liquid (volatile liquid) which has a higher surface affinity for the material than has water and a boiling point lower than that of water and then heating the slurry to a temperature below the boiling point of water but at or above that of the volatile liquid whereby the material is carried to the surface and removed therefrom. A slurry of coal is introduced into a mixing vessel 1 and then fed by a pump 2 into a vessel 5 which preferably contains an inert atmosphere, a pump 4 serving to mix with the feed naptha (the volatile liquid) drawn from a line 15 and fuel oil (an involatile liquid) drawn from a pump 19. A steam coil 20 provides the necessary heat to float the coal as agglomerages or froth for removal by a scoop 6 which feeds rotary screens 8, 9 having a discharge end extending through the end of the vessel. Naptha evaporation from the slurry is condensed in a condenser 13 cooled by a refrigerating coil 14. The ash content is drawn from the bottom of the vessel through a line 16 as a slurry and passed through a filter 17 which discharges the ash through a line 18 and returns the water to the mixing vessel 1. The addition of fuel oil at 19 serves to prevent re-wetting of the coal by water as the naphtha evaporates and to facilitate de-watering in the screens 8, 9. A surface active compound may be added in addition to, or in place of, the fuel oil for the same purpose. Furthermore, the pH of the slurry may be adjusted by the addition of lime or sodium carbonate and air or other gas used to assist flotation. Instead of the screens 8, 9 a suction filter or weir may be employed. Other volatile liquids which may be used include benzene, benzene homologues, straight chain hydrocarbons and naphthenes. The involatile liquid (fuel oil) may be, for example, kerosene, gas oil, residual fuel oil, phenol extracts or coal tar. Flotation reagents may include oleic acid, sodium carbonate, lime, sodium ethyl xanthate, sodium alkyl sulphates, sulphuric acid, dextrin, starch, terpineol and phenol.

July 30, 1968 oss ET AL HEAT TREATMENT OF SURFACE ACTIVE REAGENTS INFLOTATION Filed June 10, 1965 GERALD MOSS EDWARD CYRIL STOCKILLINVENTORS BY WHELAN, CHASAN,

LITTON, MARX a WRIGHT ATTORNEYS United States Patent 3,394,893 HEATTREATMENT OF SURFACE ACTIVE REA GENTS 1N FLOTATION Gerald Moss, NorthOxford, and Edward Cyril Stockill, Sutton, near Eynsham, Oxford,England, assignors to Esso Research and Engineering Company, acorporation of Delaware Filed June 10, 1965, Ser. No. 462,853 Claimspriority, application Great Britain, June 11, 1964, 24,276/64; Apr. 29,1965, 18,139/ 65 7 Claims. (Cl. 241-20) ABSTRACT OF THE DISCLOSUREMinerals are separated from an aqueous slurry or suspension by adding aminor amount of selected substantially water immiscible low boilingliquids and heating the mixture above the initial boiling point of thewater immiscible liquid but below that of water so that the mineral iscarried to the surface of the slurry or suspension.

This invention relates to the recovery of coal or other minerals fromaqueous slurries and suspensions with the removal of dross material,such as ash or gangue, from them. The invention is particularly suitedto the recovery of coal, although, as will be seen from the followingdescription, it is not limited to coal recovery but may be applied toother minerals such as ores in general for example bauxite, phosphaterock, fluorspar, iron ores, copper ores, lead ores and zinc ores.

Amongst the objects of the invention are to improve and cheapen theremoval of water from the aqueous slurries and suspensions aforesaidand, at the same time, to remove dross from the minerals such as theremoval of ash and other impurities from coal, and gangue from ores.

In the invention there is added, to the aqueous slurry or suspension ofthe coal, or other mineral matter, a minor amount of a substantiallywater immiscible organic liquid, or liquid mixture (hereinafter referredto as the volatile liquid) which has a higher surface affinity for thecoal or other mineral than has water, and which volatile organic liquidor liquid mixture, or a substantial proportion thereof, has a lowerinitial boiling point than the boiling point of water. The slurry orsuspension to which the volatile organic liquid, or liquid mixture hasbeen added, is then heated to a temperature below the boiling point ofwater, but at, or above, the initial boiling point of the volatileorganic liquid whereby that portion of the feed material which has beenwetted by the volatile organic liquid is carried to the surface of theslurry or suspension from which it may be recovered in known manner.

The separated mineral may be collected on a simple sieve or screen or byfiltration, according to the particle size of the separated mineralmatter; vacuum filtration may be used if considered necessary ordesirable.

It is preferred that the separation be carried out in a continuousmanner and the ratio of mineral to water by weight, in the slurry orsuspension being fed into the flotation chamber, is suitably between 1:1and 1:20, the ratio being limited on one hand by the pumpability of theslurry and the effect of dilution on the efliciency of separation, andon the other hand by the water consumption of the process.

In cases in which the major part of the mineral matter is caused tofloat, it is possible to use relatively concentrated slurries orsuspensions since the capacity of the flotation chamber may berelatively large giving a long holdup time for the tailings which willbe at a lower concentration than the floatable mineral matter ice sothat the incoming slurry or suspension is diluted on entering theflotation chamber.

The slurry or suspension preferably contains not more than 50% solids byweight, advantageously less than 25%, and the mineral particlespreferably do not exceed 1000 microns mean diameter. Whilst the averageparticle size of mineral may be as high as 800 microns it is preferablyin the range from 50 to 400 microns.

The volatile organic liquid used to treat the aqueous suspension of coalor other mineral matter preferably comprises a petroleum hydrocarbonboiling in the light naphtha range, e.g., a light virgin naphtha havinga boiling range from below F. to a temperature not exceeding 300 F.,although other organic water immiscible liquids having a higher surfaceaffinity than water for the mineral particles and having a lower initialboiling point than water, may be used; examples of other suitableorganic liquids are benzene, benzene homologues, solvent naphthas,straight chain hydrocarbons and naphthenes although it will beappreciated that other organic liquids having the specified propertiesmay be used. The volatile organic liquid is present preferably in anamount to provide not less than 1% by weight, based on the weight of thecoal or other mineral in the aqueous slurry or suspension, before theheating step is applied; particularly preferred is 5 to 25% by weightbased on the weight of the coal or other mineral. The slurry orsuspension may also contain a minor proportion of a hydrocarbon oil ofmuch lower volatility, e.g. kerosene, a gas oil, or a residual fuel oil,which remains associated with the mineral, particularly with coal,during the whole of the process and prevents re-wetting of the mineralby water as the more volatile organic liquid evaporates.

The aqueous suspension or slurry may be treated with the volatileorganic liquid by simple mixing, e.g., in a. conventional mixing vesselwith a stirrer, but the treatment is preferably effected by in linemixing in a suitable conduit leading to a vessel in which the mixture isthen heated to cause flotation of the coal or other mineral. Mixing maybe conducted at any convenient temperature below that which wouldinitiate substantial vapourisation of the volatile organic liquid andambient temperatures have been found to be suitable.

The solid matter which floats to the surface of the aqueous slurry orsuspension may then be separated and collected by any suitable meanse.g., by allowing it to spill over a weir, or by scooping it upcontinuously and then draining it on a screen, or by suction on afilter.

Using a light virgin naphtha having an initial boiling point below 100%F. it has been found sufllcient to heat the treated suspension to atemperature in the range from 100 to F. to cause flotation of the coalor other mineral. Any volatile organic liquid, e.g. naphtha, whichevaporates from the mixture during the process may be condensed andrecirculated.

As previously stated it has been found advantageous to add to certainsystems, particularly those containing coal, preferably dissolved in thevolatile organic liquid carrier, a proportion of an organic liquid ofhigher boiling point than water, e.g. kerosene, a gas oil or a residualfuel oil, hereinafter referred to as involatile organic liquid. i {-HIThe involatile organic liquid serves two useful purposes; it not onlyreduces the loss of coal or other mineral matter retained duringflotation in the aqueous phase but it also facilitates dewatering of thecoal or other mineral matter which has been floated.

The amount of involatile organic liquid that it is advantageous to usewill vary "according to the quality and particle size of the coal orother mineral dispersed in a the slurry and it may be in the range of upto wt. percent based on the weight of coal or other mineral matter.

Particularly suitable involatile organic liquids have been found to be,for example, residual fuel oils of 3,500 S.S.U. viscosity at 100 F.;other suitable oils may include for example gas oils, phenol extracts,kerosene and coal tar.

It is also within the purview of the invention to use in the slurry,together with the volatile organic liquid, either with or without theinvolatile organic liquid, minor amounts of compounds used in mineralflotation techniques which are known to those skilled in the art andreferred to as Flotation Reagents. Such reagents are described forexample in Introduction to the Theory of Flotation, Klassen andMokrousov, Classification of Flotation Reagents, Table 20, p. 154(Butterworth). These reagents may include, for example, oleic acid,sodium carbonate, lime, sodium ethyl xanthate, sodium alkyl sulphates,sulphuric acid, dextrin, starch, terpineol and phenol.

It has been found thus that the mixing energy required to cause wettingof coal or other mineral particles by the volatile organic liquid can besubstantially reduced, and the loss of combustible material can also bereduced, by adding to the mixture 21 surface active compound whichfacilitates wetting of the particles by the volatile organic liquid andwhich helps to prevent re-wetting of the mineral by water. The surfaceactive agent may be added in addition to, or in substitution for, theinvolatile organic liquid previously referred to and is preferablyemployed in concentrations of up to 0.2% by weight based on the weightof the mineral in the slurry or suspension. In the case of bituminouscoals which have been stored in a pulverised condition, the use ofanionic surface active compounds, which may he soluble in either theaqueous or organic phase of the mixture, has been found particularlysuitable. Thus the stirring time necessary to reduce the loss ofcombustible solids to the same level has been found to be less by afactor of at least 5 when 0.002 weight percent by weight (based on watercontent of the mixture) of an anionic detergent (active ingredient) isadded to the mixture. Moreover the absolute value of the loss ofcombustible solids can be reduced by a factor of at least 2 by the sameaddition. The volatile organic liquid used to obtain these comparisonswas a light virgin naphtha containing a minor proportion of a 3,500S.S.U. viscosity fuel Oil.

It has also been found that adjustment of pH of the aqueous mineralslurry with such reagents as lime or sodium carbonate can be beneficial,but the limits of pH can vary since the optimum pH range is governedlargely by the nature of the solid particles.

It may also be found advantageous for air or other suitable gas to beintroduced into the flotation system to assist the flotation of solidparticles.

The nature of the invention is further illustrated by the followingexamples:

EXAMPLE I To a coal/water slurry containing by weight of coal, having anaverage particle size of 230 microns, a particle size range of 40 to 700microns and an ash content of 16.4% by weight, was added (by weight ofthe coal) of a light virgin naphtha having the followingcharacteristics.

Degrees Fahrenheit Initial boiling point 85 Distillation:

90% 201 Final boiling point 297 The mixture was stirred thoroughly for 1minute at 50 F. The mixture was then heated to 120 F. when agglomeratesfloated to the surface of the suspension and were scooped off andcollected on a sieve. The separated coal contained 20 to 25% water byweight of the coal, and had an ash content of 10.2% by weight.

EXAMPLE II A similar procedure to that of Example I was carried out on acoal of similar particle size distribution, but having an ash content of28.3% by weight, using various quantities of light virgin naphtha asshown below. The following results were obtained:

Percent LVN added (by weight 01 the cool) Ash content of product(Percent by weight of coal) The water content of the products was againbetween 20 and 25% by weight of the coal.

EXAMPLE III A similar procedure was carried out of the same coal as inExample II, using 25% LVN (based on the coal) containing small amountsof a fuel oil of 3500 sec. nominal S.S.U. viscosity at 100 F. Thefollowing results were obtained:

Percent fuel oil Product (based on wt.

of coal) Water content Ash content (by wt. of coal) (by wt. of coal) Itwill be seen that lower water contents were obtained, due to preventionof re-wetting of the coal particles, when fuel oil was used.

EXAMPLE IV Percent Percent of total coal Ash content, percent LVN by wt.of coal added (by wt. Floated Unwetted Floated Unwettcd of coal) EXAMPLEV A similar procedure was carried out on the same coal as in Example IVusing various quantities of LVN together with various amounts of thesame fuel oil as used in Example III. Very much less coal remainedunwetted as shown by the following results where the amount of coalunwetted is indicated by the amount of combustible material lost in theash.

Product Percent Percent Percent LVN fuel oil combustible Ash Water addedadded material lost content content,

percent percent All percentages are by weight based on the coal.

In test A of this example there was insutficient LVN to cause completewetting of the coal. In test C, which corresponds to Example IV theabsence of fuel oil caused incomplete wetting of the coal and loss ofcoal in the unfloated material.

EXAMPLE VI A similar procedure was carried out on fine-ground coalshaving the same particle size distribution as in Example IV, but havingdifferent ash contents, using 50% LVN (based on the coal) and 5% fuel:oil (based on the coal). Froth was skimmed off as in Examples IV and Vand suction filtered. The following results were obtained:

Percent Ash content of coal Water content of Product Initial ProductEXAMPLES VIIXIV To a coal/water slurry having a pH of 7.6:02 andcontaining 20% by weight of a pulverised coal, having an averageparticle size of about microns, a particle size range up to 420 micronsand an ash content of 18% by weight, was added (in each example) a smallquantity of an anionic detergent and then 30% (by weight of the coal) ofa light virgin naphtha having the following characteristics:

Initial boiling point 84 Distillation:

Final boiling point 297 Mixing Percent Ash con- Example Detergent addedtime loss of 4 tent of or Test (min) cornbustiproduct ble solids VII0.002% TeepoY. l4. 0 5. 3 VIII do 1 5.0 6. 3 2 4. 2 6. 0 3 4.6 5. 4 9. 45. 2 3 4. 7 4. 3 8.6 5. 1 XIV 0.025% Acto 636- 3 4. 2 5. 3 A None 1 17.56.1 B... d 3 10.7 7. 3 C do 5 9. 2 6. 4

Acto 636 is an oil soluble sodium petroleum sulpho nate. P

Teepol and Aeto are trademarks.

It is clear from the above results that, whereas a mixing time of 5minutes is necessary to reduce the loss of combustible solids to below10% in the comparative tests where no detergent was added, a mixing timeof only 1 minute is required to reduce the loss to less than 5% when asmall amount of detergent is added. The ash content of the products ofthe examples and tests was not significantly affected by the addition ofdetergent. The water contents of all the products were in the range 23to 28% by weight.

EXAMPLE XV (Example of pH adjustment) To a coal/ water slurry containing20% by weight of a pulverised coal, having an average particle size ofabout 40 microns, a particle size range up. to 420 microns and an ashcontent of 18% by weight, was added a small quantity of anionic surfaceactive agent (0.06 Wt. percent active ingredients on weight of coal) andthen 30% (by weight of the coal) of a light virgin naphtha having thefollowing characteristics:

I.B.P 84 Distillation:

F.B.P 297 and 5% (by Weight of the coal) of a fuel oil of 3.500 normalS.S.U. viscosity at F. The mixture was stirred at 60 F. for 1 minute,when the procedure was followed substantially as described previouslythe flotation temperature being F.

There was added to the mixture before mixing small amounts of sodiumcarbonate to adjust the pH of the mixture, as shown below:

To a coal/water slurry containing 20 wt. percent of a pulverised coalhaving an average particle size of about 310 microns and an ash contentof 29.2% by weight, 15% (by weight of coal) of a light virgin naphthahaving the following characteristics was added:v

Initial boiling point 84 Distillation:

Final boiling point 297 The mixture was stirred thoroughly for 1 minuteat 50 F. and then heated to 120 F. when agglomerates formed on thesurface of the suspension and were removed. The following results wereobtained.

Treated coal ash, wt. percent, 3.0. Combustible losses, wt. percent,36.0.

EXAMPLE XVII The procedure given in Example XVI was repeated, exceptthat 5% weight on the coal of 3,500 S.S.U. viscosity fuel oil wasdissolved in the light virgin naphtha.

The following results were obtained.

7 8 Treated coal ash, wt. percent, 6.3. Combustible losses, the screen 7projecting through a baffle seal 11 in the end wt. percent 2.1. of theprocess vessel and protected by a hood 12. Condensed naphtha passes by aline 15 to the metering pump EXAMPLE XVIII 4 and 1s recirculated to themixing line 3. Fuel 011 1s sup- The procedure given in Example XVI wasagain re- 5 plied by the metering pump 19. The ash from the bottomPt!ated except that 5% Weight on the Coal Of a Straight fun of theprocess vessel 5 is drawn off as an aqueous slurry Petroleum gas oil wasdissolved in the light Virgin P through a line 16 and filteredcontinuously by a filter 17 The following results were obtained. whichreturns the water to the mixing vessel 1 and delivers Treated coal ash,-wt. percent, 5.5. Combustible losses, th h t 18, wt. percent 2.8. 10 Asan alternative to the screen 7 a suitable from of EXAMPLE XIX vacuumfilter drum may be employed.

The atmosphere in process vessel 5 is preferably inert and for examplemay be supplied by the exhaust from a diesel-driven heat pump whichtransfers heat from the refrigerating coil 14 to the heating coil 20.

When the mineral treated is coal, the product of the inven-tion is ade-ashed coal having a low water content and EXAMPLE XX in its preferredform consists of agglomerates containing a small amount of fuel oilwhich prevents the coal from Results of examination of the ash contentsof various 20 being rewetted by Water Thus the product of the inven- Theprocedure given in Example XVI was repeated, except that 5% weight onthe coal of kerosene was dissolved in the light virgin naphtha.

The following results were obtained. 15

Treated coal ash, wt. percent, 4.7. Combustible losses, wt. percent,5.5.

coals before and after treatment in accordance with the tion may notonly be used as f d directly to a coapburm present invention are givenbelow. In particular the results ing furnace, but may also be resuspended in water for show that coals treated, substantially in themanner detransport over 1 di e, by pipeline, the coal scribed in usinglight f naphtha P agglomerates being easily separated from the water atthe 3,500 fflel 011 volatlle aT 1d mvolatlle destination by simplescreening or filtration to give a rela- Orgahlc hqlllds respectlvelys lan fippreclable degree tively dry product. The invention is adapted tothe deremoval of Sulphur Present mamly m the form of ashing andde-watering of aqueous coal-oil slurries be- 1'1 es.

THE REMOVAL OF SULPHUR FROM COAL BY THE LVN FLOIATION PROCESS Ash,percent wt.

'Ieated Sulphur, percent wt. drynsh free Percent Inorganic Com-Untreated Coal Treated Percent Coal Untreated Treated bustlbles Coal,Sulphur Coal Coal Loss, Total Inorganic Total Removed percent wt.

A suitable apparatus for carrying out the process of the foretransportation, thus reducing transportation costs in invention in acontinuous manner will now be described proportion to the ash removal.with reference to the accompanying drawing which is a What is claimedis: diagrammatic representation of such an apparatus, by way 1. Aflotation process for removing mineral particles of example only. froman aqueous system selected from the group consist- Powdered coalcontaining a proportion of ash, and ing of slurries and suspensions ofsaid mineral particles which may be in the form of a slurry orsuspension in having a mean average diameter above about 40 micronswater, is introduced into a mixing vessel 1 containing which comprisesadding to the system a minor amount water, where it is brought to asuitable concentration of of a substantially Water immiscible organicliquid having coal in suspension. The suspension is then pumped by a ahigher surface affinity for the mineral to be removed metering pump 2 toa mixing line 3. Light virgin naphtha than Water and having an initialboiling point lower than or other suitable volatile organic liquid, isalso fed into the boiling point of water and heating the system to a themixing line 2 by a metering pump 4. This naphtha temperature below theboiling point of water but at least may contain a small proportion offuel oil, or other much as high as the initial boiling point of theorganic liquid, less volatile liquid than the naphtha. The mixture ofwhereby the mineral is carried to the surface of the slurry naphtha andaqueous suspension of coal may be agor suspension, and recovering themineral. glomerated by passage through the mixing line 1 and/or 2. Theprocess of claim 1 wherein a surface active on entry into the closedprocess vessel 5. In the vessel 5, agent is also added to said aqueoussystem to facilitate which preferably contains an inert atmosphere, itis heated the wetting of said mineral particles by said water imto anappropriate temperature by a coil 20, heated by miscible organic liquid.steam or other suiatble means, to partially evaporate the 3. The processof claim 1 wherein said mineral partinaphtha and cause the coal to floatas agglomerates or as cles comprise coal particles having a mean averagediamea froth to the surface of the aqueous liquid therein. ter rangingfrom about 50 to about 400 microns.

The floating coal is picked up by a scoop 6 which feeds 4. A process forseparating a mineral from a mixture the coal continuously to a rotatingscreen 7 comprising of the mineral and ash and gangue materials whichcoma coarse mesh region 8 and a fine mesh region 9. The prises: scoop 6and screen 7 are rotated continuously by the grinding the mixture intoparticles ranging less than motor 10. Coal agglomerates are retained onthe screen about 1000 microns in diameter;

7 but water drains back into the vessel 5. Ash from the forming a systemselected from the group consisting of coal sinks to the bottom of thevessel 5. Naphtha evaporataqueous slurries and aqueous suspensions ofsaid ing from the suspension is condensed in a condenser 13 particles;

cooled by a refrigerating coil 14. dispersing in said system liquidorganic material having De-ashed and de-watered coal retained by therotating a higher surface aflinity for the mineral particles screen 7 isdelivered as product through an extension of than water and containing alow-boiling constituent having a boiling point lower than the boilingpoint of water and a high-boiling constituent having a boiling pointhigher than the boiling point of water;

heating the system to a temperature between the boiling point of waterand the boiling point of said low- -boiling constituent, whereby saidmineral particles are carried to the surface of said system;

and recovering said mineral particles.

5. The process of claim 4 wherein said liquid organic material comprisesa hydrocarbon boiling in the light virgin naphtha range.

6. The process of claim 4 wherein said mineral is coal and saidhigh-boiling constituent is provided in an amount ranging not more thanabout 10 wt. percent based on the weight of said coal.

7. The process of claim 6 wherein the mean average diameter of said coalparticles ranges from about 50 to about 400 microns.

References Cited UNITED STATES PATENTS 1/1906 Kirby 209166 1/1917Schiechel 209-164 X 9/1918 Thomas 209166 3/ 1929 Holladay 209-166 4/1929 Fisher 209166 3/ 1938 Gillson 209166 11/1917 Scott 209-166 FOREIGNPATENTS 5/ 1886 Germany. 7/ 1956 France.

HARRY B. THORNTON, Primary Examiner.

R. HALPER, Assistant Examiner.

